Here's a breakdown:
* Guanine: This is a crystalline material that provides a shimmering or iridescent effect. It's found in fish scales, as well as bird droppings and some other sources.
* Why it's used: Guanine adds a pearly or shimmery look to lipsticks and other cosmetics like nail polish, eyeshadows, and highlighters.
* Is it always present? No. Many modern lipsticks achieve shimmer and shine through synthetic ingredients like mica, synthetic pearl, or other mineral pigments. The use of guanine has decreased due to ethical and sourcing concerns.
* How to tell if it's in a product: The ingredient list will usually say "guanine" or "pearl essence". However, ingredient labeling requirements vary by country.
* Is it vegan/vegetarian? No. Since guanine is derived from fish, it is not vegan or vegetarian.
In summary: Fish scales (specifically guanine extracted from them) *can* be used in lipstick to create a shimmery effect. However, it's not a universal ingredient, and many brands now use alternative ingredients. If you're concerned about this, check the ingredient list or look for vegan/cruelty-free certified products.